[clang][dataflow] Fix assert-fail when calling assignment operator with by-value parameter. (#71384)

The code assumed that the source parameter of an assignment operator is
always
passed by reference, but it is legal for it to be passed by value.

This patch includes a test that assert-fails without the fix.

Author: martinboehme

clang/lib/Analysis/FlowSensitive/Transfer.cpp

@@ -514,8 +514,14 @@ class TransferVisitor : public ConstStmtVisitor<TransferVisitor> {
           !Method->isMoveAssignmentOperator())
         return;
 
-      auto *LocSrc =
-          cast_or_null<RecordStorageLocation>(Env.getStorageLocation(*Arg1));
+      RecordStorageLocation *LocSrc = nullptr;
+      if (Arg1->isPRValue()) {
+        if (auto *Val = cast_or_null<RecordValue>(Env.getValue(*Arg1)))
+          LocSrc = &Val->getLoc();
+      } else {
+        LocSrc =
+            cast_or_null<RecordStorageLocation>(Env.getStorageLocation(*Arg1));
+      }
       auto *LocDst =
           cast_or_null<RecordStorageLocation>(Env.getStorageLocation(*Arg0));
 

clang/unittests/Analysis/FlowSensitive/TransferTest.cpp

@@ -2213,6 +2213,43 @@ TEST(TransferTest, AssignmentOperator) {
       });
 }
 
+// It's legal for the assignment operator to take its source parameter by value.
+// Check that we handle this correctly. (This is a repro -- we used to
+// assert-fail on this.)
+TEST(TransferTest, AssignmentOperator_ArgByValue) {
+  std::string Code = R"(
+    struct A {
+      int Baz;
+      A &operator=(A);
+    };
+
+    void target() {
+      A Foo = { 1 };
+      A Bar = { 2 };
+      Foo = Bar;
+      // [[p]]
+    }
+  )";
+  runDataflow(
+      Code,
+      [](const llvm::StringMap<DataflowAnalysisState<NoopLattice>> &Results,
+         ASTContext &ASTCtx) {
+        const Environment &Env = getEnvironmentAtAnnotation(Results, "p");
+        const ValueDecl *BazDecl = findValueDecl(ASTCtx, "Baz");
+
+        const auto &FooLoc =
+            getLocForDecl<RecordStorageLocation>(ASTCtx, Env, "Foo");
+        const auto &BarLoc =
+            getLocForDecl<RecordStorageLocation>(ASTCtx, Env, "Bar");
+
+        const auto *FooBazVal =
+            cast<IntegerValue>(getFieldValue(&FooLoc, *BazDecl, Env));
+        const auto *BarBazVal =
+            cast<IntegerValue>(getFieldValue(&BarLoc, *BazDecl, Env));
+        EXPECT_EQ(FooBazVal, BarBazVal);
+      });
+}
+
 TEST(TransferTest, AssignmentOperatorFromBase) {
   // This is a crash repro. We don't model the copy this case, so no
   // expectations on the copied field of the base class are checked.